Donald (Domnall mac Causantín) was the son of Constantine. He succeeded Eochaid and Giric and annexed Srathclyde, establishling himself as King of the Scots. He had some success against the Vikings in the West, but the North was dominated by Viking Sigurd the Mighty based in Orkney.

Donald was killed in 900, possibly murdered, at Donnattar near Stonehaven, Aberdeenshire. He was buried on Iona